Automatic titration apparatus and method



April 26, 1966 M. L. ROBINSON AUTOMATIC TITRATION APPARATUS AND METHODFiled Sept. 11, 1961 3 Sheets-Sheet l R a N1 M 2m WW W m A a a w W m NNJM W 3% \wmkwmmk v E l1% April 26, 1966 ROBlNsON 3,248,309

AUTOMATIC TI'I'RATION APPARATUS AND METHOD Filed Sept. 11, 1961 3Sheets-Sheet 2 I Q I "NM .3 if E W 66 40 'I I an 1 I I INVENTOR. 65 WIPfl/ A ,Pai/A/Jm/ April 26, 1966 M. ROBINSON 3,243,309

AUTOMATIC TITRATION APPARATUS AND METHOD Filed Sept. 11, 1961 3Sheets-Sheet 5 INVENTOR.

M/wA/ A. Pam/10m United States Patent Oflice 3,248,309 AUTOMATICTITRATION APPARATUS AND METHOD Myron L. Robinson, Monterey Park, Calitl,assignor, by

mesne assignments, to International Telephone and Telegraph Corporation,New York, N.Y., a corporation of Maryland Filed Sept. 11, 1961, Ser. No.137,347 17 Claims. (Cl. 204-1) This invention is directed toimprovements in automatic titration apparatus and, more particularly, toan improved titration apparatus employing novel titration cell designswhich provide for substantially continuous titration.

Titration systems for automatically determining the concentration of a:reactive agent present in a fluid by electrolytic generation ofreagents are well known. Generally, such titration apparatus utilizerelative complex combinations of electrical circuitry and titration celldesign to obtain a measure of concentration of the reactive agent in afluid which is being sampled. The titration cells generally haveseparated compartments which house isolated electrode units withseparate filtering and cleaning arrangements.

Such cells require an appreciable amount of electrolytic solution foroperation and are therefore relatively bulky and are not readilytransportable in their assembled form. Due in part to the volume ofelectrolytic solution required by such cell designs, the cells do notrespond rapidly to rapid changes in concentration of the reactive agent.In addition to lacking rapid response time to rapid changes inconcentration of the reactive agent such cell designs require anappreciable time to stabilize after the addition of new solution orfollowing a period of inoperation. Further, such cell designs generallydo not provide means for continuously monitoring the concentration of areactive agent present in a fluid and are relatively insensitive toconcentrations of less than one part per million.

Due to the above, such titration apparatus have proved unsatisfactoryfor processes requiring continuously operating means for detecting rapidchanges in the concentration of a reactive agent over wide ranges ofconcentration. One example of a process requiring such a type titratingapparatus is in the handling of high propellant fuels where it ismandatory for human health to be able to continuously detect thepresence of and rapid changes in concentration of dangerous noxiousvapors in ranges from one tenth part per million to at least 500 partsper million.

In view of the above, the present invention provides an automatic,continuous titration apparatus which responds rapidly to changes in theconcentration of a reactive agent over a range extending from one tenthpart per million to at least 500 parts per million.

In accomplishing this the present invention employs a simplified controlcircuit in combination with a novel titration cell design which isextremely compact and rugged and requires less than two milliliters ofelectrolytic solution for proper operation.

Briefly, the present invention in a basic form includes a titration cellhaving a small quantity of electrolytic solution containing ions of atitrating agent and means for continuously bubbling a fluid containing areactive agent along a predetermined fluid path through the solution.Positioned in the fluid path is a compact electrode assembly comprisingfirst and second generator electrodes spaced 3,248,309 Patented Apr. 26,1965 along the fluid path and first and second sensor electrodes spacedalong the fluid path and separated from the generator electrodes.Coupled to the generator electrodes are means for developing a currentsignal to generate the titrating agent from the ions at one of thegenerator electrodes. Coupled to the sensor electrodes are means f rgenerating a current signal between the sensor electrodes which is afunction of the concentration of the titrating agent in solution. Themeans for developing a current signal between the generator electrodesis responsive to the current signal between the sensor electrodes suchthat the titrating agent is only generated by the generator electrodeswhen the current signal between the sensor electrodes falls to apredetermined reference value. The genera-tor electrode current flow ismetered to provide a meassure of reactive agent concentration in thefluid.

In operation, when the fluid containing an unknown amount of thereactive agent is bubbled into the solution along the fluid path, thereactive agent fully combines with the titrating agent in the region ofthe generator electrodes. This reduces the concentration of thetitrating agent in the solution. The reduction in the concentration ofthe titrating agent in solution is sensed by the sensor electrodes andresults in a reduction in the current flow therebetween to thepredetermined reference value. A current is then developed between thegenerator electrodes to generate the titrating agent at the generatorelectrodes and increase the concentration of the titrating agent insolution. With the increase on concentration of the titrating agent insolution, the current flow between the sensor electrodes again increaseswith a cor-responding cessation of current flow between the generatorelectrodes. In this manner, since the current flows between thegenerator electrodes only when it is necessary to compensate for areduction in concentration of the titrating agent due to the presence ofthe reactive agent, the current flow between the generator electrodes-may be utilized to provide a measure of the concentration of thereactive agent in the fluid.

Thus, the present invention by continuously bubbling the fluidcontaining unknown amounts of a reactive agent through the electrolyticsolution and detecting a cur-rent flow which is a function of theconcentration of the reactive agent present in the fluid provides anautomatic, continuous titration apparatus. Due to the close alignment ofthe generating and sensor electrodes, the titration cell of theapparatus has a rugged, compact design and requires only a small amountof electrolytic solution for operation. The use of a small amount ofelectrolytic solution results in a reduction in the time required forthe generator electrodes to generate an amount of titrating agentsufficicnt to compensate for changes in concentration of the reactiveagent being bubbled into the electrolytic solution. In this manner, thepresent invention operates rapidly to detect changes in concentration inthe reactive agent and is ideally suited for use in processes where therapid continuous detect-ion over a wide range of concentrations ofdangerous noxious vapors is required.

For a more complete understanding of the automatic, continuous titratingapparatus of the present invention as well as a detailed understandingof the structural arrangement of the novel titration cell designs of thepresent invention, reference should be made to the following detaileddescription which is to be considered with the drawings, in which:

FIGURE 1 is a schematic representation of a basic form of the titrationapparatus of the present invention;

FIGURE 2 is a schematic representation of a preferred form of theautomatic titration apparatus of the present invention;

FIGURE 3 is a graphical representation of the current output from thetitration system represented in FIG- URE 2;

FIGURE 4 is a sectional view of one embodiment of the titration cell inaccordance with the present invention; and

FIGURE 5 is a sectional view of another embodiment of the titration cellof the present invention which is particularly adapted to use in thedetection of fuel vapors.

Referring specifically to the drawings, FIGURE 1 is a schematicrepresentation of a basic form of the automatic, continuous titrationapparatus of the present invention. Asrepresented, the titration systemincludes a titration cell represented generally at 10. Preferredembodiments of the titration cell 10, which may be employed in thetitration apparatus, are described in detail in connection with FIGURES4 and 5. Accordingly, for an analysis of the overall titration apparatusof the present invention, only the generic features of the titrationcells are here discussed.

As will be described in detail in connection with FIG- URES 4 and 5, thetitration cell includes an electrolytic solution containing ions of atitrating agent. The titrating agent is a substance or element whichcombines in a known proportion with a reactive agent in a fluid which isintroduced into the solution containing the titrating agent. By knowingthe amount or concentration of either the reactive agent or thetitrating agent required to reach a predetermined state of balance inthe solution the amount or concentration of the titrating agent orreactive agent respectively may be determined. In the automatictitrating apparatus of the present invention the determination of suchconcentration is arrived at automatically by a coulometric system ofelectrically generated reagents within a titration cell and anamperometric system coupled to the cell for detecting the predeterminedstate of balance in the solution at which state the current forelectrically generating the reagent is a measure of concentration.

By way of example only, bromine may be utilized as the titrating agentin the titration cell -the known or determinable rate of generation ofbromine in solution providing a means for determining the concentrationof a reactive agent in a fluid which is passed through the solution.

In brief, to determine the concentration of the reactive agent, such asby-products of sulphur or fuel vapor containing hydrazine, the ions ofthe titrating agent in solution (bromide ions) are electrolyzed togenerate a predetermined concentration of the titrating agent insolution. The predetermined concentration of the titrating agent isarrived at by sensing means which senses the concentra tion of thetitrating agent to produce a sensor current which in turn regulates thegeneration of the titrating agent. Thus, in response to additions of areactive agent to the solution which combine with and hence reduce theconcentration of the titrating agent below the predetermined level,means responsive to the sensor current are energized for generating thetitrating agent to compensate for the reduction in concentration. Bymonitoring the operation of the means for generating the titrating agentthe concentration of the reactive agent may then be determined.

To provide such means for determining the concentration of a reactiveagent in a fluid which is monitored by passing samples through theaqueous electrolytic solution, the titration cell 10, as represented,includes an electrode assembly 12 for generating the titrating agentfrom solution and sensing the concentration of the titrating agent toprovide means for determining the concentration of the reactive agent.The electrode assembly has a first generator electrode 14, a secondgenerator electrode 16, a first sensor electrode 18, and a second sensorelectrode 20. The generator and sensor electrodes are spaced from eachother along a common path denoted by the broken line 22 whichdiagrammatically represents the path of flow of the fluid which isintroduced into the cell. The fluid which is introduced into the cellbubbles through the solution to combine with the titrating agent andpass upward through the generator electrodes and sensor electrodes insuccession.

The generator electrodes 14 and 16 are coupled in series to a directcurrent source represented by the battery 24. The battery 24 preferablydevelops a voltage of three (3) or more volts and when connected to thegenerator electrodes causes a current to flow between the generatorelectrodes thereby causing the titrating agent (bromine) to be generatedby electrolytic oxidation at the generator electrode 16.

A source of potential represented by the battery 26 is coupled in serieswith the sensor electrodes 18 and 20 such that the sensor electrode 18is maintained at a negative potential relative to the sensor electrode20. The battery develops a voltage between the sensor electrodes and ispreferably maintained in a range of 0.25 to 0.5 volt. In this manner apotential difference is maintained 'between the sensor electrodes whichis just below a threshold voltage required to generate hydrogentherebetween. Accordingly, a polarizing film of hydrogen forms on thesensor electrode 18 to inhibit current flow between the sensorelectrodes. However, the polarizing film of hydrogen which is formed onthe sensor electrode 18 is readily depolarized by the presence of thetitrating agent bromine in the region of the sensor electrode 18.

Thus, bromine generated at the generator electrode 16 and bubbled upwardinto the region of the sensor electrode causes a depolarization of thethin film of hydrogen on the sensor electrode 18. The bromine iselectrolytically reduced at the sensor electrode 18 while the bromideions are electrolytically oxidized to form bromine at the sensorelectrode 20. Thus in operation, the sensor electrodes do not affect theconcentration of the titrating agent (bromine) in solution.

Due to the electrolytic oxidation and reduction at current flows in thesensor circuit which is a function of the concentration of bromine insolution. As will be described hereafter the sensor current varies froma predetermined magnitude corresponding to a predetermined concentrationof bromine with variations in concentration of bromine in solution.Thus, as a fluid containing a reactive agent is bubbled along the fluidpath 22 into the region of the electrode assembly 12, the reactive agentcombines with the bromine generated by the generator electrodes toreduce the concentration of bromine in solution. The reduction inconcentration of bromine is sensed by the sensor electrodes to produce areduction in the sensor current. The sensor current and reductionthereof is utilized in a manner hereinafter described to provide meansfor controlling current flow between the generator electrodes such thatthe generator current flow provides a direct measure of theconcentration of the reactive agent present in the fluid.

To provide means for such control of the current flow between thegenerator electrodes, the titrating apparatus of the present inventionbasically includes means 28 in series with the battery 24, which issensitive to current flow in the sensor circuit to connect anddisconnect the battery 24 from the generator electrodes. By way ofexample, the means 28 may include a switching meanssuch as a currentsensitive relay which operates to open the series path between thebattery 24 and the generator electrodes 14 and 16 when a predeterminedmagnitude of current is flowing in the sensor circuit and close theseries generator path when the magnitude of the sensor current isdecreased in response to a reduction in the concentration of thetitrating agent. Thus, the switching means operates to connect thebatte' y in series with the generator electrodes to provide a generationof bromine in solution to counteract the reduction in concentration ofthe titrating agent due to the presence of the reactive agent in thefluid being bubbled in the solution. When the concentration of thetitrating agent in solution is again suflicient to cause thepredetermined magnitude of current to flow in the sensor circuit, theswitching means operates to disconnect the battery from the generatorelectrodes. In this manner the switching means functions as a rapidacting on-off device to produce an intermittent current flow between thegenerator electrodes which provides a measure of the concentration ofthe reactive agent present in the fluid.

As illustrated, by way of example, in FIGURE 1 the switching meansincludes a current sensitive relay represented at 28. The relay 2% has acoil 30 connected in series between the battery 26 and the sensorelectrode 20 such that the sensor current passes therethrough. The relay28 also includes a fixed contact member 32 which is coupled to thegenerator electrode 16 and a movable contact member 34 for contactingthe contact 32. The relay 28 is a normally open relay and closes inresponse to a current passing through the coil 30 by causing the movablecontact member 34 to impinge the fixed contact member 32. The relay 28functions to connect and disconnect the battery 24 from the generatorelectrodes 14 and 16. Thus, when a current flows in the sensor circuit,the relay 23 is closed to disconnect the battery 24 from the generatorelectrodes while in the absence of current flow in the sensor circuitthe relay 28 is open, thereby connecting the battery 24 to the generatorelectrodes to provide means for generating bromine in the titration cell10. Accordingly, the relay 28 functions to halt the generation of thetitrating agent at a concentration for which sufiicient sensor currentflows to operate the relay. In this manner the predeterminedconcentration of the titrating agent and the corresponding predeterminedmagnitude of sensor current flow are defined.

Since current flows between the generator electrodes only so long as itis necessary to counteract the reduction in concentration of thetitrating agent due to the presence of the reactive agent, the currentflow in the generator circuit may be utilized to provide a directmeasure of the concentration of reactive agent. Thus, the generatorcurrent flow through a resistor 35 in series with the generatorelectrodes may be sensed by a meter 37 to measure the concentration ofthe reactive agent. Since the reactive agent is continuously bubblingthrough the electrolytic solution to combine with thetitrating agent, r

the measurement of concentration is on a continuous basis.

As will be described in connection with FIGURES 4 and 5, due to thestructural arrangement of the generator electrode assembly 12 thetitration cell 10 functions on a minimum of solution to respond rapidlyto changes in concentration ranging from one hundredth part per million.Thus, the detection of generator current flow by the meter 37 provides acontinuous measure of the concentration of the reactive agent which issensitive to concentrations of the order of one hundredth part permillion and responds rapidly to rapid changes in concentration of thereactive agent.

When the titration aparatus employs an extremely sensitive rapid actingrelay as the switching means the titration apparatus as represented inFIGURE 1, need only include the titration cell 10, the sensor circuitryas shown, and the relay 28 and battery 24 connected inseries with thegenerator electrodes for efificient operation. However, mostcommercially available relays are relatively slow acting and insensitiveto small changes in sensor current from the predetermined magnitude.

To aid such relays to be rapid acting and responsive to small changes incurrent flow in the sensor circuit, the

resistor 46 to a negative terminal of the battery 24, and

a base 48 coupled to the moveable contact 34 of the relay 28 and to anegative terminal of the battery 24 through a biasing resistor 50.

The current limiting circuit 38 includes a capacitor 52 coupled in aparallel circuit with a resistor 54- which is, in turn, connected inseries with a blocking diode 56 between the generator electrode 16 andthe base terminal 48 of the transistor 40. In this manner the currentlimiting circuit 38 shunts the moveable contact 34 and the contact 32 ofthe relay 28.

Due to the biasing provided by the battery 24 and the biasing resistor50, the transistor is in a conductive state when the relay 28 is openand is in a non-conductive state when the relay 28 is closed. Thus,initially when the polarizing film of hydrogen is present on the sensorelectrode 18 to inhibit flow in the sensor circuit, the relay 28 is inits normally open state. With the relay 28 open, a current signal ispulsed from the battery 24 through the parallel circuit consisting ofthe capacitor 52 and the resistor 54 to begin to charge the capacitor 52through the blocking diode 56. Current flow through the blockig diode 56and the biasing resistor in the base circuit 48 of the transistor 40causes the transistor 40 to begin to conduct a current through itsemitter-collector circuit and a current to flow between the generatorelectrodes 14 and 16. The current flow in the emitter-collector circuitis represented graphically in FIGURE 3 by the current signal rising as afunction of time from time t Due to the series connection of the battery24 between the generator electrodes, a small amount bromine (titratingagent) is generated at the generator electrode 16 and bubbled upwardthrough the sensor electrodes. As previousiy described the bromine incontacting the sensor electrode 18 causes a depolarization of thepolarized hydrogen film and results in an electrolytic reduction of thebromine at the sensor electrode 18 and a flow of current in the sensorcircuit. The sensor current flows through the winding 30 of the relay28, causing the relay 28 to close. The closing of the relay 28 by themoveable contact 34 impinging upon the contact 32 etlectively shortcircuits the current limiting circuit 38 and connects the positiveterminal of the battery 24 directly to the base circuit 48 of thetransistor 40. This causes the transistor 4% to be instantaneously cutoff as indicated in FIGURE 2 at time t by the interruption of currentflow in the emitter-collector circuit. In this manner, the battery 24 iseffectively disconnected from the generator electrodes causing acessation of bromine generation and allowing the capacitor 52 todischarge slowly through the resistor 54.

Although some of the bromine generated at the generator electrode 16 iselectrolytically reduced at the sensor electrode 18, a like amount ofbromine is developed at the sensor electrode 20. In this manner thesensor current flow does not cause a change in the bromine concentrationin the solution which is normally maintained at a low predeterminedlevel by the on-ofi operation of the relay 28. Accordingly, a currentnormally continues to flow in the sensor electrode circuit with amagnitude corresponding to the predetermined low level of bromineconcentration. However, if the fluid being bubbled through the electrodeassembly 12 contains a reactive agent which combines with bromine, thebromine concentration in solution is reduced. The reduction in bromineconcentration is sensed by the sensor electrode circuit as a reductionin sensor current flow from the low predetermined magnitude. When thesensor current falls below that required to maintain the relay closedthe relay 28 returns to its normally open condition and the transistor40 again becomes conductive in the manner described above allowingcurrent to again flow in the emitter-collector circuit as represented att in FIGURE 3. The magnitude of current flow again increases until atime t when the concentration of bromine in solutions exactly sufficientto compensate for the increase in concentration of the reactive agent.

Thus, due to the cooperative operation of the current limiting circuit38 and the transistor switch 37, a closing of the relay 24 in responseto an initial increase in concentration of the reactive agent does notresult in a sudden burst of high amplitude current flow in the generatorcircuit which might produce a generation of bromine much in excess ofthat required, thereby making the titration cell insensitive to smallvariations in reactive agent concentration which may immediately follow.Rather, a current signal is developed in the generator circuit whichincreases in magnitude until a sufficient concentration of bromine hasbeen generated to compensate for the change in reactive agentconcentration. This current limiting feature of the present invention isparticularly important in providing for stable reference operation(blank operation) of the titration apparatus in the absence of thereactive agent in solution as well as maintaining the sensitivity of theapparatus to small changes in concentration which would be masked ifunnecessarily large concentrations of bromine were generated.

The current limiting circuit and transistor switch combination furtherprovides for rapid operation of the titration apparatus in response torapidly occurring changes in concentration of the reactive agent. Forexample, in response to a first change in reactive agent concentrationafter the capacitor 52 has discharged (at the time t the relay 28immediately opens and current begins to flow from the battery 24 throughthe parallel RC network and the series diode 56. Due to this currentflow the capacitor begins to charge and a base current flows in thetransistor 40 causing the transistor 40 to begin to conduct current inits emitter-collector circuit. The current in the emitter-collectorcircuit generates bromine in the manner described above to cause therelay 28 to again close. Upon the closing of the relay 28 the capacitor52 is charged to a certain voltage level. Due to the blocking diode 56,the capacitor 52 is prevented from rapidly discharging through theshunting path provided by the closed contacts 32 and 34 and slowlydischarges through the resistor 54. Thus, if the relay 28 is againimmediately opened in response to another increase in reactive agentconcentration substantially the same voltage is impressed across theresistor 54 causing substantially the same base current to flow in thetransistor 40. Accordingly, the transistor 40 returns instantaneously tothe conductive condition present at the time t as indicated as L; andcontinues to become more conductive as increasing current flows in thebase circuit. As the transistor 40 becomes more conductive increasingamplitudes of current flow in the emitter-collector circuit. Thisprocess is continued with each rapidly occurring increase inconcentration of the reactive agent until the capacitor 52 reaches amaximum charged condition at a time t Henceforth, rapidly occurringchanges in concentration of the reactive agent produce a maximummagnitude of current flow which may be sustained for a period of timerequired to generate sufficient bromine to again bring the solution tothe predetermined level of bromine concentration.

Thus, due to the combination of the current limiting circuit 38 and thetransistor switch 37 the relay 28 is sensitive to small changes insensor current flow and operates to produce a generation of a muchlarger current flow in the generatorcircuit to rapidly counteract forrapidly occurring reductions in concentration of the titrating agent. Inthis manner the titrating apparatus of the present invention possessesan extremely rapid response time to small changes in concentration andpossesses an exceptionally wide operating range.

As described, the generator current flow through the emitter-collectorcircuit of the transistor 40 is a pulsating on-off current. Since themagnitude of the generator current during each pulse increases until thebromine generated at the generator electrodes compensates for theconcentration of the reactive agent present at that given time in'thesolution, the average amplitude of the generator current flow may beutilized as a measure of the concentration of reactive agent present inthe solution. Thus, to provide a measure of the concentration of thereactive agent the pulsating current flow in the load resistor 46 isfiltered through a filter represented at 58 to produce a voltage signalwhich is a representation of the average generator current fiow. Thevoltage signal is measured by a recording meter 60. For example, themeter 60 may be an electronic recording voltmeter which provides acontinuous graphical record of the average current fiow through the loadresistor 56.

To increase the accuracy and sensitivity of the measure of concentrationby detecting the average value of generator current flow it has beenfound desirable to increase the frequency of operation of the relay 28such that the relay opens and closes several times during each cycle oftitrating agent concentration compensation. Thus, instead of being openuntil the concentration of tit-rating agent returns to the predeterminedlevel the relay 28 opens and closes at a predetermined rate severaltimes before the concentration of the titrating agent returns to thepredetermined level. FIGURE 3 is a graphical representation of suchoperation. Such relay operation not only provides a more accurateaverage value of generator current but also eliminates any adverseeffects of small noise signals from the sensing electrodes as well ashysteresis and stricktion of the relay 28.

To provide such a rapid operation for the relay 28, a negative feedbackarrangement is coupled between a generator electrode and a sensorelectrode of opposite 'polarity. Preferably the feedback connection isthrough a series resistor-capacitor network 62 which couples thegenerator electrode 14 to the sensor electrode 20. In this manner whenthe relay 28 opens, current flow in the emitter-collector circuit of thetransistor 40 is fed back to the sensor electrode 20 through the winding30, causing the relay 28 to again momentarily close. If theconcentration of bromine in the solution has not returned to a levelwhereat sensor current flows in the sensor circuit, the relayimmediately opens and the process is repeated. This effects a rapidturn-on and off of the relay to provide reproducible cycling between theon and off conditions of the relay.

The titration system of the present invention has been describedincluding a general description of the generic features of the titrationcell design of the present invention. For a more complete understandingof the titration cell design as well as the structural features whichprovide for continuous automatic titration, reference should be made toFIGURES 4 and 5.

Referring now to FIGURE 4, there is represented in cross-section oneform of the rugged and compact titration cell design of the presentinvention which may be employed as the titration cell 10 in theautomatic continuous titration apparatus represented in FIGURESI and 2.

The titration cell illustrated in FIGURE 4 is particularly adapted tothe titration of substances such as sulfur compounds which arerelatively insoluble in aqueous solutions. To provide such selectivetitration, the titrat-ion cell includes means for thoroughly mixing thesulfur compound with the solution to completely combine with thetitrating agent in solution. In providing such sensitivity todifiicult-to-dissolve substances, the cell illustrated in FIGURE 4 isrelatively insensitive to substances which are readily soluble in anaqueous solution--such substances rapidly hydrolyzing and not enteringinto the operation of the cell.

As represented in FIGURE 4, the titration cell includes a container 63having an elongated end portion 6 4 and an adjacent end portion 66having a volume which is less than that of the end section 64. The endsection 66 is shaped in the form of a nipple having a valve arrangement68 disposed therein for draining the container 63.

Included within end section 66 of the container 63 is an electrolyticsolution represented at 69 containing ions of a titrating agent such asbromine. By way of example only, the electrolytic solution may be anaqueous acidified potassium bromide solution wherein bromide ionsconstitute the ions of the titrating agent bromine in solution.

Sealing the open end of the container 62 is a stopper member 70. Tointroduce the electrolytic solution into the container 63 a polyethylenetube 72 is disposed through the stopper 7t) and extends into thecontainer 63. Also disposed through the stopper 70 is a tube member 74.The tube member 74 may be composed of glass and extends longitudinallyWithin the container 63 into the end section 66. Fused to the end of thetube 74 is a bubbler 76. Preferably the bubbler 76 is composed ofsintered glass. Accordingly, a fluid pumped through the tube 74 diffusesthrough the pores in the sintered glass bubbler 76 and bubbles throughthe electrolytic solution 69 adjacent to the bubbler 76 to define apredetermined fluid pat-h through the solution. Bubbles of the fluidincluding small amounts of the solution foam at the surface of thesolution and rise in the container 63. In entering the end section 64,and due to the expanded volume thereof the bubbles burst and splatteragainst the sides of the container 63. The electrolytic solution whichis carried with the bubbles drips down into the solution along the sidesof the container 63 while the fluid in a gaseous state escapes throughan outlet tube 78 which extends through the stopper 70.

As represented, the outlet tube 78 includes a diagonal slot 86 facingthe stopper 79. Disposed within an end of the tube 78 is a .materialsuch as glass Wool indicated at 82 allowing trapped electrolyticsolution to drip back down into the end region 66 of the container 63.

In order to provide the electrolytic action of the titration celldescribed in connection with FIGURE 1, a compact electrode assembly 84is mounted around the bubbler 76. The electrode assembly 34 comprises apair of generator electrodes and a pair of sensor electrodes spaced inseries along the path traversed by the fluid in bubbling through theelectrolytic solution. The electrode assembly 84 includes a firstgenerator electrode 86 which preferably takes the form of a coil ofplatinum wire wrapped around the bubbler 76 at a point just below theend of the tube 74. A second generator electrode 88 in the form of anopen coil of platinum Wire, is also wrapped around the bubbler 76 in anannular recess 90 which is disposed in the surface of the bubblerimmediately above the end of the tube 74. Spaced from the generatorelectrodes are the pair of sensor electrodes 92 and 94. The sensorelectrodes are preferably positioned above the solution level in thecontainer 63: and operate by sensing the titrating agent which is foamedinto contact therewith. The sensor electrode 92 may be composed of aplatinum wire and is shaped in the form of an open coil around thebubbler and spaced approximately one-eighth inch from the generatorelectrode 88. The coil of the sensor electrode 92 may be approximatelyone-eighth inch in diameter to provide maximum con-tact with the foam.Spaced immediately adjacent to the sensor electrode 92 is the sensorelectrode 94-. The sensor electrode 94 is preferably composed of .aplatinum wire looped around bling fluid and solution as well assuflicient spacing of sensor and generator electrodes to preventelectric fields generated by the generator electrodes from affecting theoperation of the sensorelectrodes. In particular, due to the seriesspacing of the generator and sensor electrodes a fluid pumped throughthe tube 74 bubbles through the bubbler 76 and contacts the generatorelectrode 88. The fluid then bubbles upward contacting the sensorelectrodes 92 and 94- and is then emitted from the solution in the formof bubbles which rise upward toward the stopper 7 0.

The relative position of the bubbler, the sensor electrodes, and thesolution level as described above, also maintains a uniform velocity offluid flow in the region of the sensor electrode. This is of primeimportance to the operation of the titration cell designs of the presentinvention for although the presence of the titrating agent in contactwith the sensor electrodes depolarizes the hydrogen film on the firstsensor electrode to produce a sensor current which is a function of theconcentration of the titrating agent the ease of depolarization andhence the magnitude of sensor current flow is also a function of thefluid velocity past the sensor electrodes. Thus, since it is desiredthat the sensor current provide an accurate indication of only thetitrating agent concentration, it is mandatory that the rate of fluidflow remain constant.

As described in connection with FIGURE 1, the generator and sensorelectrodes are coupled to electrical circuitry external to the titrationcell to produce electrical generation of the titrating agent at thegenerator electrodes and a sensing of the concentration of the titratingagent at the sensor electrodes. In order to provide such electricalconnections a plurality of insulated electrical conductors 95 areincluded within the container 63. A conductor 95 is connected to eachelectrode and passes through a plastic tube 96 which is disposed throughthe stopper 70. Each conductor 95 is coupled to a terminal arrangement97. The terminal 97 includes a plurality of electrical connectors 98 forplug-in connection to the external circuitry of FIGURE 1. i

In this manner the sensor electrodes are coupled in series through asource of potential of the order of 0.5 volt and the generatorelectrodes are intermittently coupled in series through a source ofpotential of 3 or more volts. Thus, as described, a sensor current isdeveloped in the circuitry coupled to the sensor electrodes which is afunction of the concentration of the titrating agent in solution andprovides means for controlling the generation of a current between thegenerator electrodes to be a direct measure of the concentration of thereactive agent.

Due to the combination of the bubbler 76 and electrode assembly 78 alongthe path of the fluid which is bubbled through the solution automaticcontinuous titration is provided by the titration cell.

Due to the compact bubbler-electrode assembly arrangement the continuoustitration is provided in an extremely small volume of electrolyticsolution. For example, the voltmie of electrolytic solution in thecontainer 63 may be of the order of two milliliters or less. Thus, whenchanges occur in the concentration of the reactive agent being bubbledthrough the electrolytic solution a minimum of time is required for thegenerator electrodes to generate sufficient amounts of the titratingagent to return the sensor current to its predetermined level. Thisprovides for continuous, automatic titration which is rapidly responsiveto changes in concentration of the reactive agent.

Further, the bubbler-electrode arrangement operating on a small volumeof electrolytic solution in combination with the circuitry of FIGURE 1is highly sensitive to low concentrations of the reactive agent. Forexample, the titration cell, when utilized in a titration system such asdescribed in connection with FIGURE 1, is capable of sensingconcentrations of reactive agents down to one-one hundredth part in amillion.

Referring to FIGURE 5 there is represented in crosssection a titrationcell design of the present invention which is particularly useful intitrating substances which are readily soluble in electrolytic solutionssuch as fuel vapors containing hydrazine and its derivatives. As iscommonly known, hydrazine and its derivatives are compounds whichhydrolyze in the presence of water or water vapor and react slowly withtitrating agents such as bromine. Accordingly, it is desired to providea cell design which allows a minimum of contact of a fluid containinghydrazine with the electrolytic solution (the cell therefore beinginsensitive to relatively insoluble substance such as sulfur compounds)and a maximum contact with the titrating agent. Such a cell structure isillustrated in FIGURE 5.

As represented, the titration -cell includes a container 100 in which isdisposed an electrolytic solution represented at 102. The solutioncontains ions of a titrating agent such as bromine which combines withthe hydrazine in known proportions to provide means for determining theconcentration of hydrazine present in a fluid which is bubbled throughthe solution. Since hydrazine is readily soluble in electrolyticsolution it may be desirable to utilize a solution having a lowelectrolyte concentration and hence a low conductivity. By way ofexample only, the electrolytic solution may be an aqueous solutioncomprising 3% potassium bromide, 5% sodium citrate, and A of 1% citricacid.

As illustrated, the titration cell includes an outer tubular member 104which may be composed of polyethylene type plastic. Disposed in one endof the tubular member 104 is a stopper arrangement 106. The stopper 106includes three adjacent annular sections 108, 110 and 112 of decreasingradial dimension. The annular section 112 fits within an end of theouter tubular member 104. The annular section 110 includes an annularslot and is dimensioned to fit within a top member 114 to seal the opentop of the container 100. Positioned within the annular slot 116 is anO-ring 118 which functions to provide an airtight seal between thestopper 106 and the top member 114. The annular section 108 rests on thetop member 114 to support the stopper member 106 and the outer tubularmember 104 within the cell. The outer tubular member thus extendsdownward into the solution 102, an open end 120 of the tubular member104 being adjacent to the bottom of the container 100. v

Immediately above the open end 120 of the tubular member 104 is a slotindicated at 122 in the surface of the tubular member 104. Due to thefluid which is pumped into the compartment defined by the tubular member104 and the stopper 106 the solution 102 rises Within the tubular member104 to a point adjacent to the upper side of the slot 122. As will bedescribed in detail, this provides a limited but reproducible amount ofelectrolytic solution in the region of the electrode assembly of thetitration cell for operation therewith.

Supported by the stopper and extending longitudinally within the tubularmember 104 is a rod 124. The rod 124 may be composed of Teflon and hasan end member 126 having a concave lower face 128. Preferably, asillustrated, the face 128 is cone shaped.

Mounted within the tubular member 104 is a sleeve member 130. The sleevemember is preferably composed of a non-absorbent material such as Teflonand includes adjacent end sections 132 and 134. The end section 132 hasa larger volume than the end section 134, and fits tightly around thecircumference of the end member 126.

In this manner the end section 134 extends longitudinally within thetubular member 104 towards the bottom of the container 100, andterminates above the open end 120.

Disposed within an open end of the end section 134 is a glass plugmember 136 having a bore 138 therein. Positioned within the bore 138 isa glass rod 140. Due to capillary action, the surface of the glass rod140 is wetted to provide a communicating path for the electrolyticsolution into a chamber defined by the sleeve 130 and the end member126. Accordingly, the electrolytic solution 102 rises within the sleeveto a level substantially even with the level of the solution within thetubular member 104.

Mounted within the sleeve 130 is an inner tubular member 142. The innertubular member 142 may be composed of glass and extends longitudinallywithin the outer tubular member 104. The inner tubular member 142 isfixedly positioned within the sleeve 130 by spacers such as indicated at144 and 146 which provide a pressure fit between the inner tubularmember 104 and the end section 134 of the sleeve 130. In this manner theinner tubular member 142 is aligned with the sleeve 130 and spacedthere-from.

Dispose-d within the inner tubular member 142 is an electrode assembly148. As described briefly in connection with FIGURE 1, the electrodeassembly 148 includes four electrodes spaced from each other along apath traversed by a fluid which is bubbled through the electrolyticsolution. In this manner the fluid containing a reactive agent combineswith the titrating agent in the region of a pair of generator electrodesto reduce the concentration of the titrating agent in the solution. Thereduction in concentration of the titrating agent is sensed by thesensor electrodes through which the fluid and titrating agent arebubbled. The reduction in concentration of the titrating agent reduces acurrent flowing between the sensor electrodes to provide an indicationof the amount of reactive agent present in the fluid.

To provide such operation in the titration cell represented in FIGURE 5,the electrode assembly 148 includes a first generator electrode 150which preferably takes the form of a platinum wire coiled around theinner surface of the inner tubular member 142 adjacent to the plug 136.concentrically disposed within the first generator electrode is a secondgenerator electrode 152 preferably taking the form of a platinum wirewound in an elongated coil extending toward the end section 126 andpositioned adjacent to the plug 136. Spaced above the generatorelectrodes 150 and 152 along the inner surface of the inner tubularmember 142 is a first sensor electrode 154. The sensor electrode 154preferably takes the form of an elongated coiled platinum wire extendingfrom a point immediately above the generator electrodes to the end ofthe inner tubular member adjacent to the end member 126. Centrallydisposed along the first sensor electrode and between a pair of coils ofthe first sensor electrode is a second sensor electrode 156 which takesthe form of a single loop of platinum wire disposed around the innersurface of the inner tubular member 142. Such an arrangement ofelectrodes provides maximum electrode contact with the bubbling fluidand solution as well as isolation of the second sensor electrodes fromelectric fields generated by the generator electrodes when con nected tothe external circuitry of FIGURE 1.

To provide means for connecting the generator and sensor electrode toelectrical circuitry such as represented in FIGURE 1, electricalconductors represented at 158, 150, 162, and 164 are included. Theelectrical conductors are enclosed in plastic tubes which extend throughthe stopper 106 to a terminal 166. The terminal 166 includes a pluralityof electrical contacts indicated at 168 to provide electrical plug-inconnection for the electrodes to the externally located circuitry. Theterminal 166 is fixedly attached to the stopper 106 by a screw member170 and is covered by a plastic cap 172 which is attached to the stopper106.

As illustrated in one preferred form of the cell design of the presentinvention, portions of the conductors 164 and 158 adjacent to andconnecting the generator electrodes to the terminal 170 are exposed tothe solution external to the sleeve 130. In this manner a small amountof bromine is generated in the outer volume of the solution to oxidizeany residual unreacted reactive agent (hydrazine) which may pass intothe outer volume of solution. Where such leakage of the reactive agentis a par- 13 ticular problem a larger portion of the generator electrodemay be positioned external to the sleeve 130 or a separate coilarrangement in series with the generator electrodes may be provided.

To introduce the fluid containing unknown amounts of a reactive agentinto the electrolytic solution of the titration cell, a tube 174 extendsthrough a slot 176 in the stopper 106, a slot 178 in the cap member 172,downward into the outer tubular member 104 and into the sleeve 130 at apoint between the plug 136 and the inner tubular member 142. The end ofthe tube 174 is diagonally out such that fluid is emitted in an upwarddirection through the inner tubular member 142. The tube 174 ispreferably composed of Teflon. In this manner an inlet is provided forthe fluid which is resistant to plugging by fuel vapor and is anon-wetting arrangement for bubbling the fluid through the solution inthe inner tubular member.

Due to the cooperating structural arrangement of the electrode assemblyand the non-wetting bubbler, provided by the tube 174, uniform velocityof fluid flow is maintained in the region of the sensor electrodes toinsure that the sensor current is an accurate indication of theconcentration of titrating agent in solution.

In operation, the generator electrode 152 is maintained at a positivepotential relative to the generator electrode 150 and the sensorelectrode 156 is maintained at a positive potential relative to thesensor electrode 154. As described in connection with FIGURE 1, thetitrating agent, bromine, is generated at the generator electrode 152.The concentration of the titrating agent in the electrolytic solutionwithin the inner tubular member 142 is sensed by the sensor electrodes154 and 156 to produce a sensor current. A fluid is pumped through thetubing 174 into the sleeve 130 immediately below the inner tubularmember 142. In this manner, the fluid bubbles through the region of thegenerator electrodes within the inner tubular member 142 producing acomplete combination of the reactive agent with the titrating agent insolution. This reduces the concentration of the titrating agent insolution in bubble form therewith. The titrating agent in nor tubularmember carrying a portion of the electrolytic solution in bubble fromtherewith. The titrating agent in bubble form is electrolyticallyreduced at the sensor electrodes and the ions of the titrating agent areelectrolytically oxidized at the second sensor electrode 156 to producethe sensor current. When a reduction occurs in the concentration of thetitrating agent in solution, the sensor current falls from thepredetermined magnitude thereby providing the operation of the titratingapparatus as described in connection with FIGURE 1.

The fluid and electrolytic solution in bubble form in passing from theinner tubular member 142 strike the concave surface 128 of the endmember 126 causing the bubbles to burst. The electrolytic solutioncontaining the titrating agent is splattered onto the inner surface ofthe sleeve 130 and drips downward between the sleeve 130 and the innertubular 142 into the electrolytic solution within inner tubular member.The fluid in a gaseous state passes from a chamber defined by the sleeve130 and the end member 126 through an opening 180 in the end section 132of the sleeve 130. The fluid expands in a chamber defined by the outertubular member 104 in the stopper 106 to create a pressure in thechamber which maintains the level of the solution within the outertubular member 104 at a point adjacent to the upper end of the opening122. The fluid then bubbles through the opening 122 and hence throughthe electrolytic solution 102 to the surface thereof. The fluid passesfrom the electrolytic solution 102 through an opening 182 in the topmember 114 to the atmosphere.

The fluid in passing from the outer tubular member 104 through theopening 122, causes a pumping action to occur which not only maintains acirculation of the electrolytic solution within container and within theouter tubular member 104 but also allows electrolytic solution to bepumped through the plug 136 into the inner tubular member 142 tomaintain the level of the electrolytic solution therein. In this mannercontrolled circulation of the electrolytic solution within the titrationcell is provided to maintain uniform electrolytic concentration with thesolution.

As described above, the pressure within the chamber defined by the outertubular member 104 and the stopped 106 in conjunction with the fluidbeing pumped therethrough maintains the level of the solution within theouter tubular member 104 adjacent to the upper side of the opening 122.In this manner, only a small amount of electrolytic solution (less thanone milliliter) is exposed to the operation of the titration cell at anyone time. As described above, this provides for rapid response of thetitration cell to changes in the concentration of the reactive agent inthat only small amounts of the titrating agent need .be generated tocompensate for changes in the concentration of the reactive agent beingbubbled throng the cell.

Thus, the titration cell represented in FIGURE 5 provide means forcontinuously and automatically detecting concentrations of reactiveagents present in a fluid and through a cooperation of its electrodeassembly and the outer tubular member operates on a small quantity ofelectrolytic solution to provide a titration cell which responds rapidlyto changes in the concentration of a reactive agent being bubbledthrough the cell. Therefore, the titration cell represented in FIGURE 5is ideally suited for use in the detection of less than dangerousconcentrations of noxious vapors such as hydrazine and its derivativespresent in the handling of high propellant fuels.

Although the cell structures have been described as operating in a smallvolume of electrolytic solution, the titration cells also provideexcellent operation in larger volumes of solution where rapid responseto changes in the concentration of the reactive agents is not required.Thus, although the cell structure of FIGURE 4 has been described inconnection with a container having an end portion of reduced volume inthe region of the elect-rode assembly, the cell will function asdescribed in a larger container such as represented in FIGURE 5. Also,'to provide a small volume of electrolytic solution in the region of theelectrode assembly, the outer tubular member mixing arrangementdescribed in connection with FIGURE 5, may be utilized in combinationwith the bubbler electrode assembly of FIGURE 4 to replace or supplementthe dump and refill valve arrangement. Further, it is to be understoodthat the electrode assembly of FIGURE 5, although described inconjunction with the outer tubular member arrangement, may be utilizedin a container such as represented in FIGURE 4.

What is claimed is:

1. Continuous amperometric titration apparatus comprising: meansdefining a titrating cell having a pool of electrolytic solutiondisposed therein, the solution containing an excess of ions of atitrating agent; means including a bubbler for continuously introducinga gas having unknown amounts of a reactive agent into the electrolyticsolution to combine with and reduce the concentration of the titratingagent in solution; means for constraining the gas to follow apredetermined gaseous path through the electrolytic solution; anelectrode assembly, positioned in said titrating cell, and in saidpredetermined gaseous path, for the generation of the titrating agentfrom the electrolytic solution and for the sensing of the concentrationof the titrating agent in solution including afirst generator electrode,a second generator electrode closely spaced from the first generatorelectrode along said predetermined gaseous path, a first sensorelectrode spaced from the second generator electrode along said gaseouspath, and

a second sensor electrode closely spaced from the first sensor electrodealong said gaseous path, the first and second generator electrodes beingimmediately adjacent the first and second sensor electrodes and eachelectrode being unshield from the other electrodes; means for developinga potential difference between the first and second generator electrodessuch that the titrating agent is electrolytically formed from theelectrolytic solution at the second generator electrode; means fordeveloping a potential difference between the first and second sensorelectrodes which is insufficient to generate hydrogen from the solutionand which causes electrolytic reduction of the titrating agent to occurat the first sensor electrode and electrolytic oxidation of the ions ofthe titrating agent to occur at the second sensor electrode when thetitrating agent generated at the generator electrode passes with the gasinto contact with the sensor electrodes, the electrolytic reduction andoxidation at the sensor electrodes producing a current flow between thefirst and second sensor electrodes which is a function of theconcentration of the titrating agent in solution; means for controllingthe amount of electrolytic formation of said titrating agent, from saidpool of electrolytic solution, in response to said current fiow betweensaid first and second sensor electrodes; means for measuring the averagecurrent flow between said first and second generator electrodes; andmeans for replenishing said pool with additional electrolytic solution.

2. Continuous amperometric titration apparatus comprising: a vesselcontaining a pool of electrolytic solution, the solution containing anexcess of ions of a titrating agent; means including a bubbler forcontinuously bubbling a gas having unknown amounts of a reactive agentthrough the electrolytic solution along a predetermined gaseous path tocombine with and reduce the concentration of the titrating agent insolution; an electrode assembly including a first generator electrodemounted around the bubbler at one end thereof, a second generatorelectrode mounted around the bubbler and spaced along the bubblerclosely adjacent the first generator electrode such that gas passingfrom the bubbler and rising toward the surface of the solution enters aregion of the first generator electrode prior to contacting the secondgenerator electrode, a first sensor electrode mounted around the bubblerand spaced from the second generator electrode downstream from the firstgenerator electrode, a second sensor electrode mounted around thebubbler closely adjacent to the first sensor electrode and downstreamfrom the second generator electrode; the first and second generatorelectrodes being immediately adjacent the first and second sensorelectrodes and each electrode being unshielded from the otherelectrodes; means for generating the titrating agent from said pool atthe second generator electrode; means for developing a potentialdifference between the first and second sensor electrodes and whichcauses electrolytic reduction of the titrating agent to occur at thefirst sensor the first and second sensor electrodes which is a functioni electrolytic solution disposed therein, the solution containing alarge excess of ions of a titrating agent; means including a bubbler forcontinuously bubbling a gas having unknown amounts of a reactive agentinto the solution to combine with and reduce the concentration of thetitrating agent in solution; means for constraining the gas to bebubbled along a predetermined gaseous path through the solution to causethe reactive agent to completely combine with the titrating agent; afirst generator electrode positioned in the predetermined gaseous path;a second generator electrode spaced from and immediately adjacent to thefirst generator electrode and positioned along the predetermined gaseouspath; a first sensor electrode spaced from the second generatorelectrode along the predetermined gaseous path; a second sensorelectrode spaced from and immediately adjacent to the first sensorelectrode along the predetermined gaseous path, the first and secondgenerator electrodes being immediately adjacent the first and secondsensor electrodes and each electrode being unshielded from the otherelectrodes; a source of potential; switching means for coupling thesource of potential between the first and second generator electrodes tocause a current to flow between the generator clectrodes and oxidationof the ions of the titrating agent to occur at the second generatorelectrode to form the titrating agent fromthe solution, the titratingagent being bubbled into contact with the sensor electrodes; means formaintaining the first sensor electrodeat a predetermined potentialrelative to the second sensor electrode which is less than that requiredto generate hydrogen from the solution such that electrolytic reductionof the titrating agent occurs at the first sensor electrode andelectrolytic oxidation of the ions of the titrating agent occurs at thesecond sensor electrode when said gas containing titrating agent isbubbled into contact with the sensor electrodes, the electrolyticreduction and oxidation causing a current flow between the first andsecond sensor electrodes which is a function of the concentration of thetitrating agent in solution; means responsive to the current flowbetween the sensor electrodes for controlling the switching means tocouple the source of potential to the generator electrodes only when thecurrent flowing between the sensor electrodes reaches a predeterminedvalue; means for sensing the current fiow between the generatorelectrodes and means for replenishing said pool with electrolyticsolution.

4. A continuous amperometric titration assembly comprising: a vesselcontaining a pool of electrolytic solution, the solution containing alarge excess of ions of a titrating agent; means for introducing a gashaving unknown amounts of a reactive agent into the electrolyticsolution to combine with and reduce the concentration of the titratingagent in solution; means for constraining the gas to bubble along apredetermined gaseous path through the solution; means for withdrawingthe gas from the container after the gas has passed through theelectrolytic solution; an electrode assembly positioned in the containeralong siad predetermined gaseous path to generate the titrating agentfrom the electrolytic solution and to sense the concentration of thetitrating agent in solution including a first generator electrodepositioned in said predetermined gaseous path, a second generatorelectrode spaced from, and immediately adjacent to, the first generatorelectrode along said predetermined gaseous path, a first sensorelectrode spaced from the second generator electrode along saidpredetermined gaseous path, and a second sensor electrode spaced from,and immediately adjacent to, the first sensor electrode along saidpredetermined gaseous path downstream from the generator electrodes, thefirst and second generator electrodes being immediately adjacent thefirst and second sensor electrodes and each electrode being unshieldedfrom the other electrodes; a first source of potential coupled betweenthe sensor electrodes to maintain the first sensor electrode negativerelative to the second sensor electrode and produce a polarizing film ofhydrogen on the second sensor electrode which inhibits current flowbetween the sensor electrodes, the polarizing film being depolarized bythe presence of the titrating agent in the region of the sensorelectrodes to cause electrolytic reduction of the titrating agent tooccur at the first sensor electrode, electrolytic oxidation of the ionsof the titrating agent to occur at the second sensor electrode, and acurrent to flow between the sensor electrodes which is a function of theconcentration of the titrating agent in solution; a second source ofpotential; a transistor having an emitter-collector circuit and a basecircuit, the emitter-collector circuit being connected in series withthe second source of potential and the first and second generatorelectrodes; a normally open relay responsive to the current flow betweenthe sensor electrodes to close and couple the base circuit of thetransistor to the second generator electrode; means for biasing thetransistor from the second source of biasing potential to be conductivewhen the relay is open to connect the second source ofpotential inseries between the generator electrodes and cause electrolytic oxidationof the ions of the titrating agent to occur at the second generatorelectrode and a current to flow between the generator electrodes throughthe emitter-collector circuit; a resistor and a capacitor connected in aparallel circuit and in series with a diode between the base circuit ofthe transistor and the second generator electrode to shunt the relay,the diode being poled for series current fiow from the second source ofpotential to the base circuit to provide a current controlled circuitfor the relay; and means for sensing the current flow in theemitter-collector circuit of the transistor.

5. The apparatus defined in claim 4 including negative feedback meanscoupled between the first generator electrode and the second sensorelectrode.

6. A continuous amperometric titration cell comprising: means defining atitrating compartment having an electrolytic solution disposed therein,the solution containing an excess of ions of a titrating agent; meansfor introducing a gas containing a reactive agent into the electrolyticsolution including a tubular member extending from outside the titratingcompartment into the solution, the tubular member being terminated in aglass bubbler such that a gas introduced into the tubular member isbubbled through the glass bubbler and rises in the solution around thetubular member to define a path of gaseous flow; means for withdrawingthe gas from the titrating compartment after it has bubbled to thesurface of the solution; an electrode assembly positioned within thetitrating compartment for generating the titrating agent from thesolution and sensing the concentration of the titrating agent insolution including a first generator electrode wound around an end ofthe bubbler adjacent to the bottom of the chamber, a second generatorelectrode wound around the bubbler immediately adjacent the firstgenerator electrode along the path of gaseous flow, a first sensorelectrode wound around the bubbler along the path of gaseous flow spacedfrom the second generator electrode, and a second sensor electrode woundaround the bubbler immediately adjacent to the first sensor electrodedownstream from the generator electrodes, the first and second generatorelec trodes being immediately adjacent the first and second sensorelectrodes and each electrode being unshielded from the otherelectrodes; means for coupling the generator electrodes to a firstsource of potential such that the titrating agent is generated from theions in solution to be bubbled with the gas into contact with the sensorelectrodes; means for coupling the sensor electrodes to a second sourceof potential such that electrolytic reduction of the titrating agentoccurs at one of the sensor electrodes, an electrolytic association ofthe ions of the titrating agent occurs at the other sensor electrode,and a current flows between the sensor electrodes which is a function ofthe concentration of the titrating agent in solution; means forcontrolling the amount of electrolytic formation of said titratingagent, from said pool of electrolytic solution, in response to saidcurrent flow between said first and second sensor electrodes; and meansfor measuring the average current flow between said first and secondgenerator electrodes.

7. The apparatus defined in claim 6 wherein the -bubbler is a sinteredglass bubbler.

S. In a continuous amperornetric titration cell having means forcontinuously bubbling a gas containing a reactive agent along apredetermined gaseous path through pool of an electrolytic solutioncontaining a large excess of ions of a titrating agent, an electrodeassembly for generating the titrating agent from the electrolyticsolution and sensing the concentration of the titrating agent insolution comprising a first generator electrode positioned in saidpredetermined gaseous path, a second generator electrode closely spacedfrom the first generator electrode along said predetermined gaseouspath, means coupling the first and second generator electrodes forgenerating the titrating agent from the ions at one of said generatorelectrodes, the titrating agent being bubbled with said gas along saidpredetermined gaseous path to combine with the reactive agent, a firstsensor electrode spaced from, and immediately adjacent to, the secondgenerator electrode along said predetermined gaseous path, a secondsensor electrode immediately adjacent to the first sensor electrode andspaced along said predetermined gaseous path downstream from thegenerator electrodes, the first and second generator electrodes beingimmediately adjacent the first and second sensor electrodes and eachelectrode being unshielded from the other electrodes; means formaintaining a potential difference between the first and second sensorelectrodes to cause electrolytic reduction of the titrating agent tooccur at one of the sensor electrodes, electrolytic oxidation of theions of the titrating agent to occur at the other sensor electrode, anda current to flow between the sensor electrodes which is a function ofthe instantaneous concentration of the titrating agent in solution;means for controlling the amount of electrolytic formation ofsaid'tit'rating agent, from said pool of electrolytic solution, inresponse to said current flow between said first and second sensorelectrodes; means for measuring the average current flow between saidfirst and second generator electrodes; and means for replenishing saidtitration cell with additional electrolytic solution.

9. A continuous amperometric titration cell for use in a continuoustitration apparatus comprising: means defining an open top containerhaving an electrolytic solution disposed at the bottom thereof, thesolution containing ions of a titrating agent; stopper means for sealingthe top ofthe container; an outer tubular member coupled to the stopperto extend longitudinally toward the bottom of the container, the outertubular member having a hole in its outer surface near an open endadjacent to the bottom of the container; a rod supported by the stopperto extend longitudinally within the outer tubular member; a tubularsleeve having first and second end portions, the first end portion beingmounted tightly around the end of the rod and having a volume which isgreater than the volume of the second end portion, the first end sectionalso having a hole in its outer surface; a plug inserted into the secondend portion of the sleeve for admitting controlled amounts of thesolution within the sleeve; an inner tubular member longitudinallymounted within and laterally spaced fr-om the sleeve, one end of theinner tubular member being adjacent to the plug and the other end of theinner tubular member being adjacent to the end of the rod; a'length oftubing extending into the second end portion of the sleeve between theinner tubular member and the plug for bubbling a fluid containingunknown amounts of a reactive agent into the inner tubular member; anelectrode assembly mounted within the inner tubular member and includinga first generator electrode in the form of an elongated coil of wireextending longitudinally along the inner surface of the inner tubularmember adjacent to the plug, a second generator electrode in the form ofan elongated coil of wire closely spaced to and mounted concentricallywithin said first generator electrode, a first sensor electrode in theform of an elongated coil of wire extending longitudinally along theinner surface of the inner tubular member from a point spaced from thefirst generator electrode to the end of the inner tubular memberadjacent to the rod, and a second sensor electrode in the form of a wirelooped around the inner surface of the inner tubular member and spacedbetween a pair of coils of said first sensor electrode in closerelationship therewith; means for coupling the first and secondgenerator electrodes to a first source of potential; means for couplingthe first and second sensor electrodes to a second source of potentialto cause the titrating agent to be generated by the generatorelectrodes, and a current to flow between the sensor electrodes which isa function of the concentration of the titrating agent in solution;means for controlling the amount of electrolytic formation of saidtitrating agent, from said pool of electrolytic solution, in response tosaid current flow between said first and second sensor electrodes; andmeans for measuring the average current flow between said first andsecond generator electrodes.

10. The apparatus defined in claim 9 wherein the rod includes an endmember extending into the sleeve having a concave-like surface facingthe inner tubular member.

11. The apparatus defined in claim 9 wherein the plug is of glass andhas a slot therein into which is positioned a glass rod to provide aWetted communicating path for the solution into the sleeve.

12. The apparatus defined in claim 9 wherein the second source ofpotential develops a voltage of less than 0.5 volt.

13. A continuous amperometric titration cell for use in a continuoustitration apparatus, comprising: means defining a chamber having anelectrolytic solution disposed therein, the solution containing ions ofa titrating agent; a tubular member longitudinally mounted within thechamber such that a portion of the tubular member is immersed in thesolution; an electrode assembly mounted within the tubular memberincluding a first generator electrode taking the form of an elongatedcoil of wire extend ing longitudinally along an inner surface of thetubular member and immersed in the solution, a second generatorelectrode taking the form of an elongated coil of wire closely spaced toand mounted concentrically within said first generator electrode, afirst sensor electrode taking the form of an elongated coil of wireextending longitudinally along the inner surface of the tubular memberfrom a point spaced from the first generator electrode, a second sensorelectrode in the form of a loop of wire mounted around the inner surfaceof the tubular member and spaced between a pair of coils of said firstsensor electrode in close relationship therewith; means for extending aportion of the generator electrodes beyond the tubular member; means forcoupling the generator electrodes to a first source of potential suchthat a current flows between the generator electrodes to generate thetitrating agent from solution; means for coupling the sensor electrodesto a second source of potential such that a current flows between thesensor electrodes which is a function of the concentration of thetitrating agent in solution; and means for bubbling a fluid containingunknown amounts of a reactive agent into the chamber such that the fluidbubbles along a path defined by the tubular member to cause acombination of the reactive agent and the titrating agent to occur inthe region of the generator electrodes and a reduction in the currentfiow between the sensor electrodes to occur which is a function of theconcentra tion of the reactive agent in the fluid; means for controllingthe amount of electrolytic formation of said titrating agent, from saidpool of electrolytic solution, in response to said current flow betweensaid first and second sensor electrodes; and means for measuring theaverage current flow between said first and second generator electrodes.

14. Continuous amperometric titration apparatus comprising: meansdefining a chamber including a small quantity of aqueous electrolyticsolution disposed therein, the solution containing a large excess ofions of a titrating agent; means for continuously bubbling a gascontaining a reactive agent along a predetermined gaseous path throughthe solution; a compact electrode assembly positioned in saidpredetermined gaseous path and comprising first and second generatorelectrodes closely spaced along said predetermined gaseous path andfirst and second sensor electrodes closely spaced along saidpredetermined gaseous path, the first and second generator electrodesbeing immediately adjacent the first and second sensor electrodes andeach electrode being unshielded from the other electrodes; means coupledto the generator electrodes for developing a current signal between thegenerator electrodes to generate the titrating agent from the ions atone of the generator electrodes; means coupled to the sensor electrodesfor generating a current signal between the sensor electrodes which is afunction of the concentration of the titrating agent in the solution;and means responsive to the current signal between the sensor electrodesfor controlling the means for generating a current signal between thegenerator electrodes such that a current is generated between thegenerator electrodes only when the current signal between the sensorelectrodes falls to a predetermined value; means for sensing the currentflow between generator electrodes, and means for replenishing saidchamber with additional aqueous electrolytic solution.

15. A process for the continuous amperometric titration of an unknownamount of a substance which substance is reactive to a titrating agent,comprising the steps of:

continuously bubbling a gas, having unknown amounts of said substance tobe measured, at a substantially fixed rate, into a first region of apool of electrolytic solution containing ions of a titrating agent;

providing a potential between a first pair of closely spaced electrodesdisposed in said first region to electrolytically form titrating agent,in situ, in said first region of said pool of electrolytic solution,whereby said titrating agent and said substance are reacted;

passing the gas with any unreacted titrating agent into a second region;

providing a potential between a second pair of closely spaced electrodesdisposed in said second region to electrolytically reduce and thenelectrolytically oxidize any unreacted titrating agent thereby producinga current flow, said first pair of electrodes being immediately adjacentsaid second pair of electrodes and each electrode being unshielded fromthe other electrodes;

controlling the amount of electrolytic formation of said titratingagent, in situ, from said pool of electrolytic solution in response tosaid current flow;

measuring the average current flow between said first pair ofelectrodes; and

periodically replenishing said pool of electrolytic solution.

16. A process for the continuous amperometric titration of a substanceto be measured, which substance is reactive to a titrating agent,comprising the steps of:

continuously bubbling a gas, having unknown amounts of said substance tobe measured, at a substantially fixed rate, into a first region of apool of electrolytic solution containing ions of a titrating agent;providing a potential between a first pair of closely spaced electrodesdisposed in said first region to electrolytically form titrating agent,in situ, in said first region of said pool of electrolytic solution,whereby said titrating agent and said substance are reacted;

passing the gas with any unreacted titrating agent into a second region;

providing a potential between a second pair of closely spaced electrodesdisposed in said second region to reduce and then oxidizeelectrolytically any unreacted titrating agent and thereby producing acurrent fiow', said first pair of electrodes being immediately adjacentsaid second pair of electrodes and each electrode being unshielded fromthe other electrodes;

controlling the amount of electrolytic formation of said titratingagent, in situ, from said pool of electrolytic solution in response tosaid current flow;

measuring the average current flow between said first pair ofelectrodes; separating said electrolytic solution entrained in said gasleaving said second region from said gas, and returning saidelectrolytic solution into said pool to thereby recirculate saidelectrolytic solution; and

replenishing said pool with additional electrolytic solution containingions of said titrating agent.

17. A process for the continuous amperometric titration of a substanceto be measured, which substance is reactive to a titrating agent,comprising the steps of:

continuously bubbling -a gas, having unknown amounts of said substanceto be measured, at a substantially fixed rate, into a first region of apool of electrolytic solution containing ions of a titrating agent;providing a potential between a first pair of closely spaced electrodesdisposed in said first region to electrolytically form titrating agent,in situ, in said first region of said pool of electrolytic solution,whereby said titrating agent and said substance are reacted;

passing the gas with any unreacted titrating agent into a second region;

providing a potential between a second pair of closely spaced electrodesdisposed in said second region to electrolytically reduce any unreactedtitrating agent References Cited by the Examiner UNITED STATES PATENTS2,621,671 12/1952 Eckfeldt 204 2,624,701 1/1953 Austin 204195 2,745,8045/1956 Shaffer 204195 2,758,079 8/1956 Eckfeldt 204-195 2,928,774 3/1960 Leisey 204195 2,928,775 3/1960 Leisey 204195 2,934,693 4/ 1960Reinecke et al 204195 2,989,377 6/1961 Leisey 23230 3,032,493 5/1962Coulson et a1 204-195 3,038,848 6/1962 Brewer et al. 204195 3,131,1334/1964 Barendrecht 204-195 3,162,585 12/1964 De Ford et al. 204-195OTHER REFERENCES Lingane: Electroanalytical Chemistry, 2nd edition,1958, page 497.

Sease et al.: Analytical Chemistry, volume 19, No. 3,

March 1947, pages 197-200.

JOHN H. MACK, Primary Examiner.

JOHN R. SPECK, Examiner.

15. A PROCESS FOR THE CONTINUOUS AMPEROMETRIC TITRATION OF AN UNKNOWNAMOUNT OF A SUBSTANCE WHICH SUBSTANCE IS REACTIVE TO A TITRATING AGENT,COMPRISING THE STEPS OF: CONTINUOUSLY BUBBLING A GAS, HAVING UNKNOWNAMOUNTS OF SAID SUBSTANCE TO BE MEASURED, AT A SUBSTANTIALLY FIXED RATE,INTO A FIRST REGION OF A POOL OF ELECTROLYTIC SOLUTION CONTAINING IONSOF A TITRATING AGENT; PROVIDING A POTENTIAL BETWEEN A FIRST PAIR OFCLOSELY SPACED ELECTRODES DISPOSED IN SAID FIRST REGION TOELECTROLYTICALLY FORM TITRATING AGENT, IN SITU, IN SAID FIRST REGION OFSAID POOL OF ELECTROLYTIC SOLUTION, WHEREBY SAID TITRATING AGENT ANDSAID SUBSTANCE ARE REACTED; PASSING THE GAS WITH ANY UNREACTED TITRATINGAGENT INTO A SECOND REGION; PROVIDING A POTENTIAL BETWEEN A SECOND PAIROF CLOSELY SPACED ELECTRODES DISPOSED IN SAID SECOND REGION TOELECTROLYTICALLY REDUCE AND THEN ELECTROLYTICALLY OXIDIZE ANY UNREACTEDTITRATING AGENT THEREBY PRODUCING A CURRENT FLOW, SAID FIRST PAIR OFELECTRODES BEING IMMEDIATELY ADJACENT SAID SECOND PAIR OF ELECTRODES ANDEACH ELECTRODE BEING UNSHIELDED FROM THE OTHER ELECTRODES; CONTROLLINGTHE AMOUNT OF ELECTROLYTIC FORMATION OF SAID TITRATING AGENT, IN SITU,FROM SAID POOL OF ELECTROLYTIC SOLUTION IN RESPONSE TO SAID CURRENTFLOW; MEASURING THE AVERAGE CURRENT FLOW BETWEEN SAID FIRST PAIR OFELECTRODES; AND PERIODICALLY REPLENISHING SAID POOL OF ELECTROLYTICSOLUTION.